24/12-1

General

Well 24/12-1 is located on the Gudrun Terrace ca 15 km east of the border to British sector. The purpose of the well was to evaluate a seismic closure, named Gamma, in the southern part of the Block. The main target was the Middle Jurassic sands. Well 24/12-1 was the first of two phases in drilling the borehole, and this first phase was planned to reach the Early Cretaceous only. The main target was planned to be reached in a later re-entry with a different rig than was available at the time when the well was scheduled.

The well is Type Well for the Skade Formation and Reference Well for the Grid Formation.

Operations and results

Wildcat well 24/12-1 was spudded with the semi-submersible installation Ross Rig on 16 January 1978. At the time when the well was to be spudded, Statoil did not have available a rig equipped with a 15000 psi BOP stack and associated equipment. The well was therefore spudded with Ross Rig, which was equipped with a 10000 psi BOP. Ross Rig drilled the well down to 3966 m in the Early Cretaceous Sola Formation. The 9 5/8" casing was set and the well was temporarily plugged and abandoned. The problems experienced during PHASE I were primarily related to weather (anchor chain breakage and WOW), BOP-stack, and items lost into the hole and the sea. The well was drilled with seawater and gel from down to 771 m, with lignosulphonate mud from 771 m to 2874 m, and with lignosulphonate/lignite/CMC from 7874 m to TD. From 2870 m 1 % to 8% oil was added to the mud.

Tertiary sandstone intervals were encountered in the Utsira Formation (497 m to 730 m), the Skade Formation (825 m to 1007 m), the Grid Formation (1502 m to 1660 m), and in the Paleocene Heimdal Formation (2326 m to 2700 m). No shows were encountered during drilling, but post-well organic geochemical analyses showed one cuttings sample from 2860 m to 2890 m to contain significant amounts of light hydrocarbons combined with a comparati